This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in PCT International Application No. PCT/CH00/00065 having an International Filing Date of Feb. 7, 2000, and Swiss Patent Application No. 410/99 filed Mar. 5, 1999.
1. Technical Field
The present invention relates to a method for rounding a sheet-metal blank and a multi-roll rounding machine for carrying out the method.
2. Background Information
Rounding processes are used to bend sheet-metal parts for the manufacture of, in particular, tubular bodies, such as ducts or filter cases, which after rounding are fed to an ensuing processing station for permanent joining of the adjacent longitudinal edges. Sheet-metal blanks for the stated purpose may have various configurations, as, for example, those for ducts may have cutouts for subsequent connection of a branch pipe, or those for filter cases may be provided with a sieve structure, making processing difficult and imposing considerable demands on the rounding operation. Such sheet-metal blanks typically have a thickness of 0.3 to 3 mm, and the diameter after rounding lies between 25 and 500 mm. But thinner (or thicker) blanks are also processed by rounding machines into bodies with other diameters.
To round sheet-metal blanks of the above-described kind, e.g. three-roll rounding machines are used, with which the blanks are bent around a rounding roll as two guide rolls, spaced apart from one another but working in conjunction with the rounding roll, press the blanks against a segment of the rounding roll as the blanks pass through, so producing plastic deformation. It has been found that on a three-roll rounding machine the blank is insufficiently deformation. It has been found that on a three-roll rounding machine the blank is insufficiently rounded e.g. in the leading edge region, as, when the blank is led in, it is initially only seized between the rounding roll and the first guide roll, and is not rounded, or is not rounded sufficiently, until the leading edge reaches the second guide roll, at which point the plastic deformation process commences. This is particularly critical in the case of blanks which have a relatively large cutout at the leading edge, so that the laterally adjacent regions are then overstressed and tend to buckle.
Accordingly the two guide rolls have been reduced in diameter with a view to shortening the distance between their axes and hence the length of the region of insufficient rounding. The attendant risk of deflection of the guide rolls has been countered by a fourth roll that supports the guide rolls as a back-up roll on the opposite side to the path of the blank, and thus prevents undesired deflection. This four-roll rounding machine possesses improved characteristics, but fails to solve the fundamental problem of insufficient rounding of the leading portion of the blank.
At the end of its pass through the rounding machine, the leading edge of the blank is caught on a catch rail with suitably formed grooves, as is, after rounding is complete, the trailing edge of the blank, which then snaps onto the catch rail elastically, so that the rounded blank can be shifted along the catch rail to the ensuing processing station.
There are also known two-roll rounding apparatuses in which a sheet-metal blank is rounded between a rounding roll and a single guide roll provided with a compressively elastic coating. Unlike the above-mentioned three or four-roll rounding technique, such rounding methods do allow faultless rounding of a sheet-metal blank. If the rounding rolls are periodically moved apart during the rounding operation as feed continues without interruption, straight regions are left between the bends. For example, a sheet-metal body with a triangular profile can be produced in this way. In the present description, such designs are also called, by analogy, xe2x80x9ctubularxe2x80x9d. At the end of the rounding cycle, the leading edge is again located immediately before the point of run-in to the rounding rolls.
To obtain complete, and hence high-quality, rounding, the rounded sheet-metal parts are removed axially from the rounding roll, and are not trapped in a catch rail. A catch rail will of course be located as near to the run-in point as possible, but for geometrical reasons it may lie only approximately in the path of the leading edge, and not at the end of that path but further back. This then causes a spreading-apart of the rounded blank at the end of the rounding operation, which, in view of the precise rounding achieved by the two-roll machine and depending on the subsequent application of the sheet-metal body, is detrimental.
However, with axial withdrawal of the rounded blank, in contradistinction to the catch rail that also serves as guide rail for onward transport of the blank, the orientation of the sheet-metal body, that is to say the position of the edges to be subsequently joined, is lost. A two-roll rounding machine will therefore usually have a downstream working station that re-establishes the orientation of the sheet-metal bodies so that they can be arranged on a transport rail. A further snag with axial withdrawal, especially in the case of thick sheets, is the risk of damaging the relatively soft, and hence vulnerable, compressively elastic coating of the rounding roll. These known two-roll apparatuses have proved to be technically complex, and moreover costly.
Therefore the fundamental problem of the present invention is to specify a method for rounding sheet-metal blanks which does not have the above-stated drawbacks, that is to say one which yields and improved rounding quality combined with a definite orientation of the sheet-metal body for subsequent processing, simply and without requiring an additional processing station.
According to the present invention a method and an apparatus for rounding a sheet or plate blank in a rounding apparatus having rounding rolls is provided. A predetermined second part region of the blank is rounded after a predetermined first part region has been rounded. A feed direction of the blank for the rounding of the second part region is selected such that rounding in the second part region proceeds towards the previously rounded first part region.
For the purposes of the description of the invention, the term xe2x80x9cleading edgexe2x80x9d refers to the edge which is seized first at the run-in, and xe2x80x9ctrailing edgexe2x80x9d the opposite edge, of a sheet-metal blank making a conventional pass through a rounding apparatus. This terminology will be retained even where the leading edge is actually trailing because the feed direction has been reversed in accordance with the invention. xe2x80x9cForward feedxe2x80x9d is the direction in which the blank is [moving when] seized by its leading edge at the run-in point, while the opposite direction is called xe2x80x9creverse feedxe2x80x9d.
The effect of rounding part regions of the sheet-metal blank one after the other in a specific way, namely by running in opposite directions, is that the edges are brought to a final position that is not the same as with the conventional methods.
For example, with conventional methods, the leading edge, as stated, runs around the guide roll through a full 360xc2x0, owing to the one-way feed of the rounding apparatus; which also corresponds to the intention of producing a tubular body by a 360xc2x0 rounding process, and then of joining the adjacent edges. After rounding, the leading edge is again located immediately before the run-in to the rounding rolls.
If the method according to the invention is used, the final position of the edges of the rounded body is different: When rounding of the second part region commences in the direction towards the first part region, the leading edge moves away from the run-in point, and runs backwards along its path. Complete rounding can be obtained with the edges in a universal and predeterminable position. This means that a catch rail can be positioned where there is no subsequent distortion of the perfectly rounded blank, with the result that the orientation of the blank is not lost, and an ensuing processing station is not needed.
In a preferred embodiment, the whole blank is rounded in two part regions. In the first part region, rounding proceeds from the leading edge to the center of the blank; the rolls are then parted until the trailing edge of the blank (whose feed continues) reaches the run-in point. With reverse feed, rounding of the second part region is then performed from the trailing edge towards the first part region. When the center of the blank is reached again, rounding is complete. The center of the blank, not the leading edge, now lies at the run-in point, and the edges lie opposite this point, on the other side of the rounding roll.
The effect of the embodiment which has been described above is obtained by rounding the second part region in accordance with the invention after the first part region has been formed. The direction of feed during rounding of the first part region is immaterial; it would be feasible to propel the blank through spaced-apart rolls as far as its center, to close the rolls, and then to round the first part region from the center to the xe2x80x9cleadingxe2x80x9d edge. The direction of feed during rounding of the first and second part regions would then be the same.
These and other objects, features, and advantages of the present invention will become apparent in light of the detailed description of the present invention.